This invention relates to roadway traffic control and, more particularly, to a method and apparatus for displaying the status of a system of traffic signals.
A time-space diagram is used by traffic engineers to design timing plans in an coordinated arterial traffic control system. Such a time-space diagram is a two-dimensional graph representing distance along the arterial in the horizontal coordinate and time in the vertical coordinate. Vertical traffic signal interval bands are drawn on the distance coordinate at the signalized intersections. Across the graph is drawn a horizontal working line on which the green or red phase of each traffic signal interval band is centered. A traffic progression speed line which has a slope representing the desired progression speed through the arterial is drawn with an origin at the beginning of the green phase of the first intersection in the system. For each succeeding intersection, either a red or green signal phase is centered on the horizontal working line to obtain an equal band width for each direction of flow.
Computer programs have been developed to reduce the expenditure of labor on, and to improve the accuracy of, timing plan designs.
A number of computer controlled graphic displays have been used to date to represent wide area traffic control conditions. One such graphic display is a static time-space representation of the cycle at each intersection, corrected for travel time to eliminate the need for proportional spacing of intersections. Another graphic display is a static representation of traffic density throughout a system in time and distance; the result is a platoon progression diagram showing the traffic distribution in the system as a function of time. A third graphic display dynamically represents the status of traffic signals in a system; the traffic signals are represented on the display at positions spatially coordinated with the signalized intersections and the traffic signal representations on the display change color as the traffic signals sequence through their cycle.